256869 research outputs found
Sort by
Comparison of muscular activity and metabolic response between a novel handle-based and a push-rim wheelchair in a simulated daily mobility circuit
No full textPush-rim wheelchairs are widely used but are associated with low energy efficiency and a high risk of upper limb overuse injuries. To address these issues, we developed a novel handle-based wheelchair aimed at reducing joint strain and improving propulsion efficiency. This study compared muscular and metabolic demands between handle-based and push-rim configurations during an everyday wheelchair course. 22 healthy, wheelchairnaive participants completed a course, including ramps obstacle avoidance, and directional changes, using 3 wheelchair configurations: 1 handle-based and 2 push- rim setups with different wheel sizes. Electromyographic recordings and continuous cardiopulmonary data were collected. The handle-based system resulted in a redistribution of muscle activity, with reductions in several key propulsion muscles and an overall decrease in metabolic demand compared with push-rim propulsion. These fin-
dings suggest that the handle-based wheelchair may offer a more energy-efficient and joint-friendly alternative to conventional push-rim designs, with potential benefits for long-term mobility and upper limb healt
Clean and Prosperous Uganda (CPUg) – Fecal Sludge and Solid Waste Management for Improved Livelihoods
No full textHedin-Vertex berechnet durch Exakte Diagonalisierung von Hubbard-Clustern
No full textAntiferromagnetic spin fluctuations are a prime suspect for the superconducting glue in cuprates and nickelates. The minimal model reproducing the main physics of these systems is the single-orbital Hubbard model. Diagramatically, the scattering of electrons with these spin fluctuations can be described via a three-point propagator, where the coupling between these two quasiparticles - the propagator with amputated legs - is the Hedin vertex in the magnetic channel, or spin-fermion vertex. It has previously been shown that this coupling shows a rich dependence on fermionic momentum, notably a divergence close to half filling at the antinode. Exact diagonalization calculations for finite clusters in this work reproduce this momentum dependence. Furthermore, the known power law relation from DCA results between the Hedin vertex and the self-energy is also observed. Finally, a physical interpretation of the Hedin vertices' pole at the antinode, due to its established equivalence to the derivative of the self-energy w.r.t to an applied magnetic field is discussed for the 4x4 cluster
Eigenschaften epitaktisch hergestellter LaCrO3-Dünnschichten durch Sputterdeposition
No full textDiese Masterarbeit untersucht epitaktisch gewachsene Lanthanchromat-Dünnschichten (LaCrO3, LCO), die mittels Radiofrequenz (RF) Magnetronsputtering auf verschiedenen Perowskitsubstraten unter definierten epitaktischen Spannungszuständen hergestellt wurden. Im Mittelpunkt steht dabei die detaillierte Analyse ihres elektronischen Transportverhaltens. Zu Beginn war es infolge einer Relokalisierung des Equipments notwendig, das verwendete Sputtersystem vollständig neu aufzubauen, zu kalibrieren und in Betrieb zu nehmen, um eine hohe Kristallqualität und reproduzierbare Wachstumsbedingungen zu gewährleisten. Eine strukturelle Charakterisierung mittels Röntgenbeugung, Röntgenreflektivität, reziproker Raumabbildungen und Rasterkraftmikroskopie bestätigte ein kohärentes epitaktisches Wachstum sowie eine ausgeprägte Stufen-Terrassen-Morphologie der Oberflächen.Während alle unter epitaktischer Spannung gewachsenen Filme, wie auch das entsprechende Bulkmaterial, elektrisch isolierend sind, zeigen temperaturabhängige Widerstandsmessungen ein metallisches Verhalten für LCO Filme auf TiO2-terminierten SrTiO3 (STO) Substraten. Dieses wird auf die polare Diskontinuität an der LCO/STO-Grenzfläche zurückgeführt. Darüber hinaus treten im Aufwärmzyklus der Messungen bei bestimmten Temperaturen ausgeprägte Anomalien im Widerstandsverlauf auf, deren Stärke sowohl von der verwendeten Temperaturänderungsrate während der Messung als auch vom nachträglichen Annealing der Filme beeinflusst wird. Diese Anomalien zeigen sich weitgehend unabhängig von äußeren Magnetfeldern und deren Orientierung, was auf elektronische oder ionische Relaxationsprozesse an der Grenzfläche beziehungsweise auf defektbedingte Mechanismen als deren Ursache schließen lässt. Magnetischen Messungen werden vom Diamagnetismus des STO-Substrats sowie von ferromagnetischen Beiträgen aufgrund von Verunreinigungen im gleichen Substrat dominiert, sodass die Antiferromagnetismus-Signatur der LCO Filme nicht eindeutig erkennbar ist. Insgesamt weisen die Ergebnisse darauf hin, dass grenzflächeninduzierte Ladungsumverteilungen maßgeblich zum metallischen Verhalten der LCO/STO-Heterostrukturen beitragen.This Master thesis investigates epitaxial lanthanum chromate (LaCrO3, LCO) thin films grown by radio-frequency (RF) magnetron sputtering on perovskite substrates under various strain conditions. Particular attention is given to the detailed analysis of the transport behaviour. To that end, due to the relocation of the equipment, the sputtering system first had to be reassembled, calibrated, and commissioned to ensure high crystalline quality and reproducible deposition conditions. Structural characterisation using X-ray diffraction, X-ray reflectivity, reciprocal space mapping and atomic force microscopy confirmed coherent epitaxy and step–terrace surface morphology. Whereas all strained films grown on different substrates are insulating, consistent with bulk LCO, temperature-dependent resistivity measurements reveal a metallic-like behaviour for LCO films grown on TiO2-terminated SrTiO3 (STO) substrates. This is attributed to the existence of a polar discontinuity at the LCO/STO interface. Additionally, upon warming up, distinct upturns in resistivity are observed at characteristic temperatures, whose amplitude and shape depend on the temperature sweep rate and the post-deposition annealing. These features are found to be largely insensitive to magnetic field and its orientation, suggesting an origin related to interfacial or defect-driven electronic and ionic relaxation processes. The magnetic measurements are dominated by the diamagnetism of the STO substrate, as well as some ferromagnetic contributions from impurities in the same substrate, preventing to discern the antiferromagnetism of the LCO films. Altogether, the results suggest a scenario in which interface-driven charge redistribution plays a key role on the emergent metallic behaviour of LCO/STO heterostructures
Edge fluctuation measurements in EDA H-mode and QCE plasmas in ASDEX Upgrade using the correlation electron cyclotron emission diagnostic
No full textThe requirement of a plasma solution without large edge-localized modes (ELMs) for future fusion devices motivates the study of plasmas without Type I ELMs. The enhanced D–α (EDA) and quasi-continuous exhaust (QCE) scenarios are two such Type I ELM free plasmas, but their underlying physics principles are not fully understood. A database of EDA and QCE plasmas from ASDEX Upgrade was compiled and analyzed using the correlation electron cyclotron emission diagnostic in order to study differences between properties of the quasi-coherent mode (QCM) between these two regimes. Investigations into measured spectral properties of the QCM, radi- ated temperature fluctuations δTrad/Trad, and radial correlation lengths Lc showed no differences between the two regimes. Spectral properties using the cross-power spectral density, Gxy were sim- ilar between regimes, with the values measured to be a central frequency, fQCM ≈ 20 − 50 kHz; spectral width, ∆f ≈ 5 − 40 kHz; δTrad/Trad ≈ 4 − 6%; and Lc ≈ 1 − 2 cm. Investigations into a quantity representing the relative bandwidth ∆f/fQCM revealed differences between EDA and QCE plasmas when plotted radially, suggesting some type of interaction between the QCM in QCE plas- mas with the surrounding broadband turbulence that is not present in EDA phases. Additionally, investigations into various drive terms for hypothesized instability drivers for the QCM are per- formed showing no difference in the parameter spaces of collisionality and the ion temperature, electron temperature, or electron pressure scale lengths between each regime indicating that there is no observable difference between the drive behind the QCM in each regime
Experimental analysis of nonlinear vibration absorbers using real-time hybrid simulation
Get PDFDie Beherrschung mechanischer Schwingungen ist entscheidend für Leistungsfähigkeit, Sicherheit und Lebensdauer moderner technischer Systeme. Bei unerwünschten Schwingungen habensich neben klassischen Strategien wie Systemverstimmung, Dämpfung und Isolierung vor allem Schwingungstilger als wirkungsvolles Mittel zur Amplitudenreduktion etabliert. Weist eine Hauptstruktur nichtlineares Verhalten auf, müssen auch die Tilger nichtlinear ausgelegt werden. Dabei können komplexe Phänomene wie amplitudenabhängige Frequenzverschiebungen, Sprungphänomene,innere Resonanzen sowie isolierte Lösungen in Frequenzgängen auftreten, die kritische Schwingungsamplituden erzeugen und dadurch die Struktur sogar gefährden können.Ziel dieser Arbeit war es, nichtlinearen Tilger-Hauptstruktur-Systeme mit Duffing-Charakteristik umfassend zu analysieren, optimale Parameter zu bestimmen, Grenzen der Tilgerwirkung aufzuzeigen und Risiken durch nichtlineare Effekte zu identifizieren.Zur Untersuchung nichtlinearer Schwingungen wurde ein echtzeitfähiger Hybrid-Testprüfstand entwickelt, der reale Tilger über ein geregeltes Übertragungssystem mit virtuellen Hauptstrukturen koppelt. So lassen sich nichtlineare Phänomene experimentell nachbilden, beliebig initialisieren und systematisch analysieren, ohne reale Strukturen zu gefährden. Die innovative hybride Analyse verbindet analytische Modellbildung, numerische Simulation einschließlich Stabilitäts und Bifurkationsanalyse sowie experimentelle Validierung und eröffnet damit einen integrativen Ansatz für Forschung und Anwendung.Die Arbeit zeigt, dass zahlreiche analytische und numerische Methoden zur Analyse nichtlinearer Phänomene existieren, experimentelle Untersuchungen jedoch bislang nur in geringem Maße verfügbar sind. Mit dem entwickelten Prüfstand kann diese Lücke teilweise geschlossen und zentrale Methoden validiert werden. Die numerischen Grundlagen umfassen die Shooting- und die Harmonische-Balance-Methode, das Bogenlängen-Fortsetzungsmethode sowie die Floquet-Theorie. Ergänzt durch Testfunktionen zur Identifikation von Bifurkationspunkten, gelingt eine zuverlässige Vorhersage und gezielte Untersuchung isolierter Lösungen.Die experimentellen Ergebnisse bestätigen, dass die optimalen Parameter der generalisierten Equal-Peak-Methode gut mit Versuchsdaten übereinstimmen. Darüber hinaus konnte erstmals gezeigt werden, dass isolierte Lösungen in Frequenzgangflächen durch simultane Anpassung von Erregeramplitude und -frequenz oder durch präzise Umschaltstrategien erreicht und analysiert werden können.Abschließend werden Einschränkungen und Perspektiven diskutiert, denn die physikalischen Grenzen des Übertragungssystems sowie die Beschränkung auf Strukturmodelle mit polynomialen Kennlinien begrenzen das Spektrum möglicher Anwendungen. Gleichzeitig verdeutlichen die Ergebnisse den praktischen Nutzen, etwa für die Entwicklung robuster Tilger und ihre Anwendung in Maschinenbau und Bauwesen. Perspektiven liegen in der Erweiterung auf Systeme mit mehreren Freiheitsgraden, der Analyse von Multi-Tilger-Konfigurationen sowie in fortgeschrittenen Regelungskonzepten.Insgesamt leistet die Arbeit einen wesentlichen Beitrag zur Weiterentwicklung experimenteller Methoden der nichtlinearen Schwingungstechnik. Die Validierung der Equal-Peak-Methode und die erstmalige direkte, gezielte experimentelle Erreichung von isolierten Lösungen stellen zentrale wissenschaftliche und praktische Ergebnisse dar, die neue Wege für die robuste Auslegung und Optimierung nichtlinearer Schwingungstilger aufzeigen.The precise control of mechanical vibrations is essential for the performance, safety, and servicelife of modern engineering systems. Beyond classical strategies such as detuning, damping, and isolation, vibration absorbers have proven effective in reducing resonant amplitudes. If the host structure exhibits nonlinear behaviour, the absorbers must also be designed with nonline arrestoring forces. This gives rise to complex phenomena such as amplitude-dependent frequency shifts, jump phenomena, internal resonances, sub- and superharmonics, and isolated solutions infrequency response functions, which may lead to critical vibration amplitudes and endanger the structure. The objective of this work was to analyse nonlinear absorber–host structure systems with Duffing-type characteristics, to determine optimal parameters, to identify limits of absorber performance, and to detect potential risks associated with nonlinear effects.To achieve this, a real-time hybrid test bench was developed in which physical absorbers were coupled to virtual host structures via a controlled transfer system. This approach enabled theexperimental generation, systematic tracking, and detailed measurement of nonlinear phenomena without endangering real structures. The methodology combines analytical modelling, numerical simulation, stability and bifurcation analysis, and experimental validation, thereby establishingan integrated framework for research and application.The study shows that while a wide range of nonlinear phenomena can be analysed usinganalytical and numerical methods, experimental investigations have so far been limited. Thedeveloped test bench helped to close this gap by validating established design methods andenabled the direct investigation of phenomena that are hardly accessible with conventionalapproaches. The numerical analysis relied on shooting methods, harmonic balance, continuationtechniques, and Floquet theory. Complemented by test functions for detecting bifurcation points,this provided a reliable framework for predicting and analysing isolated solutions.Experimental results confirmed that the optimal parameters predicted by the generalised equal-peak method were in close agreement with those obtained from measurements. Moreover,it was shown for the first time that isolated solutions can be reached using force-controlled experiments, either by simultaneously varying excitation amplitude and frequency or by applying dedicated switching strategies. This allowed a direct and systematic investigation of isolas infrequency response surfaces.Finally, the limitations and perspectives of the method were discussed. Constraints a rose from the physical limits of the transfer system, the restriction to simplified single-degree-of-freedom models, and the restriction to polynomial restoring forces. Nevertheless, the results highlight thepractical relevance for the design of robust absorbers and their application in mechanical andcivil engineering. Future research should extend the methodology to multi-degree-of-freedomhost structures, multi-absorber configurations, and advanced control strategies.In conclusion, the work makes an important contribution to the experimental investigation ofnonlinear vibration phenomena. The validation of the generalised equal-peak method and the firstdirect force-controlled experimental realisation of isolated solutions represent key scientific and practical results, paving the way for the reliable design and optimisation of nonlinear vibration absorbers
A satellite-based assessment of ERA5 soil moisture and land surface temperature interannual co-variability
No full textLand surface temperature provides a fingerprint of the surface energy balance. Under similar radiative forcing, particularly during daytime and clear-sky conditions, its temporal variability is expected to be coupled to surface conditions such as availability of soil moisture and plant functional conditions. In this study, we use Earth observations to identify regions with a strong interannual co-variability between the diurnal amplitude of land surface temperature and surface soil moisture. Land surface temperature is taken from the European Organization for the Exploitation of Meteorological Satellites Applications Facility on Land Surface Analysis and soil moisture from the Copernicus Climate Change Service for the period 2004–2023 over the 0° Meteosat Second Generation region, encompassing Africa and Europe. We introduce a new metric to quantify the soil moisture-temperature interannual co-variability in the satellite data, which is then applied to evaluate the fifth reanalysis from the European Centre for Medium-Range Weather Forecasting (ERA5). Earth observations and ERA5 show similar spatial co-variability patterns across much of the domain, highlighting regions of transition between climate zones. However, ERA5 shows weaker co-variability in regions with large interannual vegetation variability. These findings suggest that accurately capturing the interannual variability of land surface temperature and its co-variability with soil moisture, in regions with large vegetation variability, may require a dynamic representation of vegetation status, beyond the mean annual cycles currently implemented in ERA5
Evaluating human–machine collaboration through a comparative analysis of experts, machine learning, and hybrid approaches in real estate valuation
No full textAccurate prediction of real estate prices remains a major challenge due to dynamic market conditions
and the limitations of traditional valuation methods. Empirical studies that directly compare human
experts, machine learning (ML) models, and hybrid approaches are rare. This study examines the
predictive accuracy and efficiency of an XGBoost-based ML model, real estate experts, and a hybrid
human–machine approach. A model was trained using 21,736 real estate transactions from Vienna
(2018–2022). We then conducted an experimental procedure with 13 experts who evaluated newly
built apartments sold in 2023 under three conditions: limited information, state-of-the-art expert
methods, and collaboration between experts and ML model. The results show that the ML model
achieves accuracy comparable to that of experts while significantly reducing the time required for the
task. Within the hybrid approach, experts were able to achieve the highest accuracy in comparison to
other methods. These results underscore the potential of human-ML collaboration
